Passive acoustics for monitoring bottom contact of dredge

In Argentina, stock assessment of Patagonian scallop (Zygochlamys patagónica) is carried out applying the swept area method using a dredge. Hence, for the accuracy of the biomass estimation contact of the dredge with the bottom is critical. Generally during these surveys the dredge contact with the bottom is determined by taking into account warp length/bottom depth relationship and vessel speed. These reasons motivated the study of the feasibility of monitoring, in a synoptic way, the chronology and dynamics of the fishing gear by means of the acquisition of sounds generated during the fishing operations. Sound recordings were acquired using a low cost, homemade self-contained hydrophone attached to the mouth of the dredge. Using this acoustic device it was possible to register the contact time of the dredge with the bottom in 60 fishing operations. This information could be used to monitor, in an easy way, the performance of the fishing gear during scallop stock assessment.